Radio shielded spark plug



' H. RABEZZANA RADIO SHIELDED SPARK PLUG Fued July 15. 1940 Aprii 15, 1941.

v nentor do @Mezzana Patented Apr. 15, 1941 2.238.391 nsnlo Summen smak VPLUG.

Hector Babezzana. Flint, Mich., assigner to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 15, 1940, Serial No. 345,476

3 Claims.

My invention relates to radio shielded spark plugs designed to prevent high tension current supplied to the insulated electrode of a spark plug from interfering with the operation of adjacent radio receiving apparatus; and the same comprises improved metallic shielding features associated with and enclosing the supply conductor leading to the insulated electrode of the plug, and which shield is conductively connected to the engine structure so that electrical waves, due to high tension oscillating current in the supply lead, are grounded bythe shield and prevented from being radiated into the adjacent space. Specifically, my invention consists in improved terminal connector features for providing a conducting path through which current is supplied to the insulated electrode of the plug, in providing better insulation than heretofore between the high tension supply conductor and the grounded shell or casing of the plug, and in otherwise improving radio shielded spark plugs as hereinafter and at lengthappears. The drawing accompanying and forming a part of this speciflcation illustrates the preferred form of my invention, and therein:

Figure 1 is a view showing a section of my improved radio shielded spark plug taken upon a central plane extending longitudinally thereof.

Figure 2 is a view showing a section upon a transverse plane indicated by the line 2-2, Figure 1, upon a much larger scale.

Referring now to the drawing, my improved shielded spark plug comprises a hollow tubular shell or casing 5 made commonly of low carbon or machinery steel, and the lower end of which is externally threaded at 6 to screw into a threaded hole in the wall of an internal combustion engine cylinder. The upper end of this shell is threaded to receive the threaded lower end of a metallic shield tube l which in effect is a part of the casing, and the upper end of this shield tube is threaded to receive a coupling member 8 whereby a current supplying lead 9 may be con-` nected to the spark plug. The supply lead includes as a part thereof an external metallic sheath I0 which ordinarily extends throughout the-length of the supply lead and forms a conducting shield or casing therefor which is grounded to the engine with which the plug is used through the coupling member 8, the shield, tube I and the shell or casing of the plug. The sheath Il may be in the form of tubing as shown, or in the form of a braided or woven' covering for the lead in which case it is commonly associated with a terminal nipple with which member engages to secure the lead to the tubular casing l.

Within and extending throughout the length of the casing 5 is a tubular insulator II made from porcelain or equivalent ceramic or dielectric material suitable for withstanding the high temperature and strains met with in spark plugs; saidinsulator having an inclined shoulder I2, and being supported by an internal ledge I3 within the shell 5. This insulator is held in place within the casing l5 by a still.' but resilient holding gasket or washer I4 lC-shaped in cross section, and commonly made of spring steel and acting between an annular washer I5 at the upper end of the insulating member I I, and an internal annular ledge I8 within the shield tube 1; and

,which c-shaped.- washer is compressed and distorted and subjected to stress which acts to force the insulating member downward and toward the ledge I3 as the shield tube 1 is screwed into the upper end of the casing 5. Thernumerall'l des- I of the engine, so that the temperature of the insulated electrode I9 and of the insulator II will be kept as low as possible. The lower end of the cooling sleeve has a metallic gasket I8 U- shaped in cross section which is clamped between shoulder I2 and the ledge I3, and which acts to hold the sleeve I1 in place and to provide a gas-tight packing between the insulating member and the shell of the plug. The insulated electrode I8 is in the forni" of a bevel-headed screw having a threaded portion 20 at its upper end as shown, which screws into a similar threaded portion at the upper end oi' the passage provided; for the electrode in the insulating member II; a suitable gasket 2l being commonly provided between the inclined head 22 of the electrode and thefinsulating member to seal the joint between the electrode and the upper end of the passage through which it extends.

The numeral 23 designates a tubular member made of Abakelite or equivalent insulating mate-- the coupling the metallic shield 1 when the supply lead is connected to the plug through this terminal member. Said upper end' has a passage into which the supply lead 9 enters and within which it tits closely, the terminal or tip being in eiect a part of the supply lead and coming away there: with when said lead is disconnected from. the plug. The upper end of the member 23 extends to the upper end of shield tube 1 of the plug and the same is held` in place within the plug structure, and the supply lead 9 is secured to the plug, by the coupling member 3; this being accomplished: in the embodiment of my invention illustrated by providing the metallic casing Il with an internal ledge 23 which overlies the upper extremity of the member 23 so that the act of vscrewing the coupling member onto the shield tube forces the terminal member downward and secures the supply lead to the plug structure; the

terminal member, as hereinbefore pointed out,

being in edect a unitary .part of the supply lea/d.

The current supply lead e comprises a metallic conductor iii of small diameter surrounded by comparatively thiclr insulation 2U of rubber or like material; and the conductor has a terminal comprising a head 3u of ball or like form and an extension 3i shaped like a cork-screw and which,

with upper surface oi' the head end 22 of the insulated electrode I9. The parts 32', 33'and 34 are 4permanently' assembled .with the terminal mem-7 ber 23; and although the detachable connection provided by the socket 33 and head 30 permits the supply lead 9 to be pulled out of the passage in the member 23 into which it extends without difilculty and another lead to be substituted therefor, it is contemplatedfthat the terminal member 23 shall remain assembled with the current supply lead 3 so as to form permanently attached terminal or tip therefor as hereinbefore explained.

` In assembling the insulating member Il with the shell 5 and shield tube 1 the tube is screwed' into the upper end of the shell, thus compressing and stressingthe c-shaped gasket I4, after which the shell is subjected to longitudinal .compression while a thin wall section 36 thereof is heated 'by a current of electricity made vto flow therethrough, thus providing a more perfect gas-tight Joint between the upper end of the insulating member and the shield tube; and it will be appreciate'd that two concentric insulating members both extending beyond the upper end of the shell or casing i are present in my improved shielded plus, one being the upper end of the insulating member I l and the other being the lower end of the terminal member 23.

Having thus described an'd explained my lnvention, I claim and desire to secure by Letters Patent:

1. In a shielded spark plug, a hollow tubular shell or casing having a threaded portion at its lower end, and a metallic shield tube extending upwardly therefrom; a tubular insulating memberl supported within said shell or casing and extending into the lower end of said shield tube; means for securing said insulating member in place within-said shell; an insulated electrode carried by and extending from. the lower end of said insulating member; a tubular terminal member made of insulating material within said shield tube and extending downward and into said insulating member; an insulated current supply lead extending into the upper end of said terminal member, and which lead has an external metallic sheath; means for securing said metallic sheath to the upper end of said shield tube; and means permanently assembled with said tubular terminal member for providing a. current conducting connection between said supply lead and said insulated electrode.

2. In a shielded spark plug, a hollow tubular shell or casing having a threaded portion at its lower end, and ametallic shield tube extending upwardly therefrom; atubular insulating member supported within said shell or casing and extending into the lower 'end of said shield tube; means for securing said insulating member in place within said shell; an insulated electrode carried by and extending from the lower end of.

said insulating member; a tubular terminal member made of insulating material Within said shield tube and extending downward and into said insulating 'membem an insulated current supply lead extending into the upper end of said terminal member, and which lead has an external metallic sheath; a ledge extending inwardly from said metallic sheath, and which ledge overlies the upper end of said tubular terminal member; a coupling member engaging the upper end of said shield .tube and the lower end of said metallic sheath to thereby secure said sheath to said tube; and means permanently assembled with said tubular terminal member for providing a current conducting connection between said supply lead and said insulated electrode.

3. In a shielded spark plug, a hollow tubular shell or casing having a threaded portion at its lower end, and a metallic shield tube extending upwardly therefrom; a tubular insulating member supported within said shell or Ycasing and extending into the lower end of said shield tube; means for securing said insulating member in place within said shell; an insulated,electrode carried by and extending from the lower end of said insulating member; a tubular terminal member made of insulating material within said shield tube and extending` downward and into said insulating Amember; an insulated current supply `secured to the upper end of said rod and adapted to clasp said head, to thereby provide a detachable connection between said rod and said head;

and means for providing a current conducting connection between the lower end of said rod and 

